Temperature‐ and E‐field‐dependent domain configuration and electrical properties in (K,Na, Li)(Nb,Ta, Sb)O3 single crystal

E‐field‐ and temperature‐dependent domain evolution of lead‐free tetragonal (K, Na, Li)(Nb, Sb, Ta)O₃ (KNLNTS) single crystals as well as its corresponding electrical properties have been investigated. When E field is applied along [011]_C direction, (2T) engineered domain structure is formed. Spontaneous polarizations switch under a critical electric field (around 4‐5 kV/cm), resulting in significant changes in domain structure and great improvement in piezoelectric properties. Furthermore, it is found that piezoelectric constant d₃₁ and electromechanical coupling factor k₃₁ of [011]_C poled KNLNTS single crystal decrease with temperature. The extrinsic and intrinsic piezoelectric responses are discussed from the viewpoint of domain structure and lattice distortion, respectively. Our results show that the nanodomain structure relaxes and the lattice distortion declines with temperature, resulting in reduction of extrinsic and intrinsic piezoelectric responses, respectively. Therefore, the piezoelectric instability is ascribed to the decrease of both extrinsic and intrinsic contributions. This work provides a better understanding of domain engineering technique, and the useful information on the improvement of both piezoelectricity and temperature stability of the lead‐free piezoelectric materials.     

Secondary phase softening effect in PZT-based ceramics by introducing the random electric fields

In this work, the random electric fields are constructed in the hard PZT ceramics by adding the ZnO particles as a secondary phase to tune the piezoelectric properties and losses. It is found that the internal bias electric field existing in the hard PZT ceramics has been tuned successfully by the random electric fields and its value reduces with the increased ZnO content. As a consequence, the piezoelectric constant d₃₃ reaches up to 483 pC/N in the PZT/0.75 wt%ZnO composite, which is much higher than that of the hard PZT matrix. In the meantime, the electromechanical quality factor Q_m, dielectric loss tan δ, and Curie temperature T_C for this composite are about 1109, 0.55%, and 279°C, respectively. The promoted d₃₃ is attributed to the small domain size and reduced internal bias electric field, whereas the low losses (large Q_m and low tan δ) can be put down to the still existing nonzero internal bias electric field.     

Sb2O3-modified lead zirconate titanate piezoelectric ceramics with enhancing piezoelectricity and low loss

Lead zirconate titanate (PZT)–based piezoelectric ceramics as important functional materials are widely used in many electromechanical devices. The piezoelectric coefficient and mechanical quality factor are vital property parameters for piezoelectric applications. However, the piezoelectric coefficient is inversely proportional to the mechanical quality factor, resulting in a strong limitation among wide applications. Herein, piezoelectric ceramics composed of (xSb₂O₃, 0.3-wt% MnCO₃)-doped (Pb_0.92Sr_0.08)(Zr_0.533Ti_0.443Nb_0.024)O₃ ((xSb, Mn)-PSZTN) were prepared by a conventional solid-state process. The excellent piezoelectric properties d₃₃ = 554 pC/N, k_p = 0.645, and high mechanical quality factor Q_m = 540 were simultaneously obtained at x = 0.1 ceramic in the morphotropic phase boundary region. The enhancement of piezoelectric properties was mainly due to the contribution of irreversible domain wall motion. In particular, the regulation of different defect chemical reactions on the properties showed that Sb₂O₃ could play the role of both donor and acceptor dopant. This work demonstrated that (0.1Sb, Mn)-PSZTN ceramic was a good candidate material for high-power piezoelectric devices.     

Achieving both high electromechanical properties and temperature stability in textured PMN-PT ceramics

Textured piezoelectric ceramics, such as textured Pb(Mg_1/3Nb_2/3)O₃-PbTiO₃ (PMN-PT) ceramics, have attracted considerable attention from both academia and industry, as they possess crystal-like piezoelectric properties, high composition homogeneity, and low manufacturing cost. However, the main difficulty with the textured piezoelectric ceramics is the presence of BaTiO₃ (BT) templates, which greatly reduces their piezoelectricity and phase transition temperature. Thus, it is highly recommended to fabricate textured piezoelectric ceramics using as few templates as possible. Here, we successfully fabricated high-quality <001>-textured PMN-28PT ceramics (texturing degree of 99%) by using an extremely small amount of BT templates (1 vol.%) with the help of CuO/B₂O₃ sintering aids. The textured PMN-28PT ceramic exhibits 80% piezoelectric coefficient (d₃₃ ∼ 1200 pC/N), 96% electromechanical coefficient (k₃₃ ∼ 88%) and the same temperature stability (T_rt ∼ 100, T_c ∼ 150°C) when compared to its single crystal counterpart. In addition, by using an alternating current electric field poling (AC-poling), the piezoelectric coefficient d₃₃ and dielectric permittivity ε₃₃ of the textured PMN-28PT ceramics were further enhanced around 5–8%. It is believed that the advantages of high electromechanical properties, low cost, and easy mass production of textured PMN-28PT ceramic will make it a promising candidate for advanced electromechanical devices.     

Significantly enhanced dc electrical resistivity and piezoelectric properties of Tb-modified CaBi2Nb2O9 ceramics for high-temperature piezoelectric applications

Bismuth layer–structured ferroelectric calcium bismuth niobate (CaBi₂Nb₂O₉, CBN) is considered to be one of the most potential high-temperature piezoelectric materials due to its high Curie temperature T_c of ∼940°C, but the drawbacks of low electrical resistivity at elevated temperature and low piezoelectric performance limit its applications as key electronic components at high temperature (HT). Herein, we report significantly enhanced dc electrical resistivity and piezoelectric properties of CBN ceramics through rare-earth element Tb ions compositional adjustment. The nominal compositions of Ca_1−xTb_xBi₂Nb₂O₉ (abbreviated as CBN-100xTb) have been fabricated by conventional solid-state reaction method. The composition of CBN-3Tb exhibits a significantly enhanced dc electrical resistivity of 1.97 × 10⁶ Ω cm at 600°C, which is larger by two orders of magnitude compared with unmodified CBN. The donor substitutions of Tb³⁺ ions for Ca²⁺ ions reduce the oxygen vacancy concentrations and increase the band-gap energy, which is responsible for the enhancement of dc electric resistivity. The temperature-dependent dc conduction properties reveal that the conduction is dominated by the thermally activated oxygen vacancies in the low-temperature region (200–350°C) and by the intrinsic conduction in the HT region (350–650°C). The CBN-3Tb also exhibits enhanced piezoelectric properties with a high piezoelectric coefficient d₃₃ of ∼13.2 pC/N and a high T_c of ∼966°C. Moreover, the CBN-3Tb exhibits good thermal stabilities of piezoelectric properties, remaining 97% of its room temperature value after annealing at 900°C. These properties demonstrate the great potentials of Tb-modified CBN for high-temperature piezoelectric applications.     

High-power piezoelectric energy harvester produced using [0 0 1]-textured (Na,K)NbO3-based lead-free piezoceramics

High-power piezoelectric energy harvesters (PEHs) require piezoceramics with a large k_p and d₃₃ but small ε^T₃₃/ε₀ values. The [0 0 1]-textured 0.96(Na, K)(Nb_1−xSb_x)–0.04SrZrO₃ piezoceramics (x = 0.025 and 0.045) exhibited the improved electromechanical coupling factor (k_p) and piezoelectric charge constant (d₃₃); however, the increase of dielectric constant (ε^T₃₃/ε₀) was not significant. Further, the textured piezoceramic with x = 0.045 shows the large d₃₃ × g₃₃ value of 21.5 pm²/N, where g₃₃ is piezoelectric voltage constant, indicating that texturing is a good technique to fabricate the piezoceramics for PEH. The impedance curve of the PEH consisting of the metal substrate and textured piezoceramic shows a piezoelectric resonance peak at a low frequency, which is the same as the mechanical resonance frequency of the PEH. Hence, the PEH can be considered a piezoelectric material. The figure of merit of the PEH was determined using the mechanical quality and electromechanical coupling factor calculated from the impedance curve of the PEH. A large power output of 1.7 mW was obtained from the type-1 PEH at the resonance frequency produced using the textured thick film (x = 0.045). Hence, this PEH can be used as a permanent power source for microelectronic devices in the Internet of Things.     

Large Area Thick Films of PVDF‐TrFE and Relaxor‐Ceramics for Piezo‐ and Pyroelectric Applications

Wearable electronics, sensors, and energy harvesting devices are gaining an ever increasing importance in consumer products. Their success is, however, contingent on the availability of flexible and cost‐effective functional materials. The present paper presents an up‐scaled processing route for 0–3 thick film composites of the ferroelectric polymer polyvinylidenefluoride‐trifluoroethylene and a relaxor ceramic. Different compositions are investigated for pyro‐ and piezoelectric applications. Various samples are produced via tape casting and spin‐coating as freestanding and supported films of up to 600 × 200 mm² and on 150 mm silicon wafers, respectively. The samples are characterized in terms of thickness and roughness reproducibility, mechanical properties, and impedance. It is shown that good reproducibility and quality of the films can be realized. Depending on the application targeted (pyroelectric or piezoelectric), specific compositions together with the suitable poling process are presented. For instance, a composite with 24 vol% ceramic shows highest pyroelectric properties together with lowest piezoelectric thickness coefficient (d₃₃) when poled for pyroelectric applications. On the other hand, a composite with 50 vol% ceramic exhibits a d₃₃ of 100 pm V^?1 that is unsurpassed for this type of composites. These properties are advantageous in a large variety of applications, including wearable devices.     

Strong electromechanical coupling in paraelectric KTa1‐xNbxO3 crystals

A rare electromechanical resonance excited by a weak (<10 V/mm) alternating‐current electric field alone is observed in paraelectric KTa_1‐xNb_xO₃ crystals near the Curie temperature. We show that the transformation from a disordered to an ordered polar‐nanoregion arrangement under the electric field enhances the electrostrictive effect near the phase transition, leading to strong electromechanical coupling. This result establishes the fundamental correlations between the polar nanoregions and the macroscopic physical properties in relaxor ferroelectrics.     

Simultaneously achieving high energy storage performance and low electrostrictive strain in BT-based ceramics

Dielectric ceramics with high recoverable energy storage density (W_rec) and high energy storage efficiency (η) are urgently needed due to their potential application in pulse capacitor devices. However, the low  η and breakdown strength (BDS) have produced a bottleneck for achieving high W_rec at high electric field. Here, we introduce Bi(Mg_0.5Ti_0.5)O₃ (BMT) into Ba(Ti_0.92Sn_0.08)O₃ (BTS) matrix to enhance the relaxor character of BTS–xBMT and reduce the electrostrictive strain generated during electric field loading. The enhanced relaxor character is beneficial for increasing the efficiency, whereas the reduced electrostrictive strain is profitable to increase the BDS. Furthermore, the BDS is significantly improved by the polymer viscous rolling process. Finally, the electrostrictive effect was considerably lowered in an optimized BTS–0.1BMT composition. More crucially, a high W_rec of 4.34 J/cm³ was attained accompanied by excellent temperature stability (variation ≤±5% between 30 and 120°C). The current results show that the developed dielectric ceramics can be used in pulse capacitor devices for energy storage.     

Characterization of acceptor-doped (Ba,Ca)TiO3 “hard” piezoelectric ceramics for high-power applications

Acceptor Mn or Co-doped Ba_0.925Ca_0.075TiO₃ (abbreviated as BCT-Mn and BCT-Co) lead-free piezoelectric ceramics with high density and fine grains were synthesized by conventional solid-state reaction method. The phase structure and electrical properties of the ceramics were investigated. The acceptor-doped BCT ceramics were found to exhibit asymmetrical polarization-electric field hysteresis loops corresponding to the presence of an internal bias field E_i, indicating that the domain walls were pinned by preferentially oriented defect dipoles formed by the acceptors and oxygen vacancies. High mechanical quality factor Q_m and low dielectric loss tanδ were obtained for the ceramics due to the strong internal bias field (E_i =4–5kV/cm). In particular, BCT-Mn ceramics exhibited the best properties, with mechanical quality factor Q_m =1020, dielectric loss tanδ=0.2% and piezoelectric coefficient d₃₃ =190 pC/N. Furthermore, the planar electromechanical coupling factor k_p for BCT-Mn ceramics was found to be larger than 0.4 in the temperature range of 25 °C to 75 °C. These results indicate that the Mn-doped BCT lead-free ceramics material is a promising candidate for high-power piezoelectric applications.     

Ferroelectric,piezoelectric and electrostrictive properties of Sn4+‐modified Ba0.7Ca0.3TiO3 lead‐free electroceramics

Lead‐free Ba_0.7Ca_0.3Ti_1?xSn_xO₃ (x=0.00, 0.025, 0.050, 0.075, and 0.1, abbreviated as BCST) electroceramic system was prepared by the solid‐state reaction method and its ferroelectric, piezoelectric, and electrostrictive properties were investigated. X‐ray diffraction shows that the compositions with x≤0.05 exhibit a tetragonal crystal structure having P4mm symmetry; while the compositions x=0.075 and 0.1 exhibit a mixed P4mm+Amm2 phase coexistence of tetragonal and orthorhombic and P4mm+Pmm pseudo‐cubic lattice symmetries, respectively, at room temperature. The dense microstructure having relative density ~90%‐92% and average grain size in the range ~2.36 μm to 8.56 μm was observed for BCST ceramics. Temperature‐dependent dielectric measurements support the presence of phase coexistence and show the decrease in Curie temperature (T_C) with Sn⁴⁺ substitution. The dielectric loss (tan δ) values in the temperature range (?100°C to 150°C) was observed to be <4%, for all BCST ceramics. The BCST compositions exhibit typical polarization‐electric field (P‐E) hysteresis and electric field induced strain (S‐E) butterfly loop, which confirms the ferroelectric and piezoelectric character. The compositions x=0.025, 0.05 and 0.075 show the peaking behavior of displacement current density () to an applied electric field () (J‐E) which implies the saturation state of polarization. The maximum electrostrictive coefficient (Q₃₃) value of 0.0667 m⁴/C² was observed for x=0.075 and it is higher than some of the significant lead‐based electrostrictive materials. The compositions x=0.05 and 0.075 exhibit the notable electrostrictive properties that may be useful for piezoelectric Ac device applications. The observed results are discussed and correlated with the structure‐property‐composition.     

Static fatigue behavior of cracked piezoelectric ceramics in three-point bending under electric fields

This paper describes an experimental and analytical study on the static fatigue behavior of piezoelectric ceramics under electromechanical loading. Static fatigue tests were carried out in three-point bending with the single-edge precracked-beam specimens. The crack was created perpendicular to the poling direction. Time-to-failure under different mechanical loads and dc electric fields were obtained from the experiment. Microscopic examination of the fracture surface of the piezoelectric ceramics was performed as well. A finite element analysis was also made, and the applied energy release rate for the permeable crack model was calculated. The effect of applied dc electric fields on the energy release rate versus lifetime curve is examined. The most important conclusion we reach is that the lifetimes for the piezoelectric specimens under a positive electric field are much shorter than the failure times of specimens under a negative electric field for the same mechanical load level.     

Ultra-high-temperature piezoelectric responses and ultra-high thermal stability of piezoelectricity in ceramic PbZr0.54Ti0.46O3

To date, most piezoceramics with a high piezoelectric coefficient (d₃₃ > 500 pC/N) and a high Curie temperature (T_C around 400°C) are BiScO₃-PbTiO₃-based (BS-PT-based) systems, containing the rare-earth element Sc, whose high cost hinders mass production. We investigated the effect of Nd-doping on the morphotropic phase boundary and synthesized low-cost Nd-doped PbZr_0.54Ti_0.46O₃ (PZT) piezoceramics, achieving high piezoelectric performance. At room temperature, the piezoelectric coefficient d₃₃ reached 550 pC/N with a T_C = 375°C and this changed by only 3.6% over a broad temperature range (30–260°C). The d₃₃ value reached an ultra-high value of 941 pC/N at 345°C, which is higher than that of a BS-PT-based ceramic (810 pC/N at 350°C). The developed PZT ceramic material has a superior electrostrictive strain of 0.45% at 40 kV/cm, and a room temperature piezoelectric coefficient d₃₃* of 1312 pm/V at 20 kV/cm. Our research provides a new paradigm for designing piezoceramics that can be used over a wide temperature range.     

Temperature‐insensitive piezoelectricity in lead‐free NaNbO3‐based ceramics

In this work, we report a lead‐free piezoelectric ceramic of (0.9‐x)NaNbO₃‐0.1BaTiO₃‐xBaZrO₃, and the effects of BaZrO₃ on the phase structure, microstructure, electrical properties and temperature stability are investigated. A morphotropic phase boundary‐like region consisting of rhombohedral (R) and tetragonal (T) phases is constructed in the compositions with x = 0.035‐0.04. More importantly, in situ temperature independence of the piezoelectric effect {piezoelectric constant (d₃₃) and strain} can be achieved below the Curie temperature (T_c). Intriguingly, the electric field‐induced strain is still observed at T ≥ T_c due to the combined actions of the electrostrictive effect and the electric field‐induced phase transition. We believe that NaNbO₃‐based ceramics of this type have potential for applications in actuators and sensors.     

Investigation of MnO2‐doped (Ba,Ca)TiO3 lead‐free ceramics for high power piezoelectric applications

x% mol MnO₂‐doped Ba_0.925Ca_0.075TiO₃ ceramics (abbreviated as BCT‐Mnx, x=0‐1.5) were synthesized by conventional solid‐state reaction method. The effects of MnO₂ addition and (Ba+Ca)/Ti mole ratio (A/B ratio) on the microstructure and electrical properties of the ceramics were investigated. The internal bias filed E_i was determined from the asymmetrical polarization hysteresis loops and found to increase with the doping concentration of MnO₂. High mechanical quality factors (Q_m>1200) and low dielectric loss (tanδ<0.5%) were found in the BCT‐Mn0.75 and BCT‐Mn1.0 ceramics with E_i>3 kV/cm, meanwhile, the piezoelectric and electromechanical properties were found to decrease compared with the pure BCT, exhibiting a typical characteristic of “hard” behavior. Of particular interest is that the microstructure of BCT‐Mn0.75 ceramics could be controlled by changing the A/B ratio, where enhanced piezoelectric coefficient d₃₃ on the order of 190 pC/N was obtained in the BCT‐Mn0.75 ceramics with A/B=1.01 due to its fine‐grained microstructure, with yet high Q_m, being on the order of 1000. The high d₃₃ and Q_m in MnO₂‐doped BCT ceramics make it a promising candidate for high power piezoelectric applications.     

Effect of Composition on the Electromechanical Properties of (1-x)Pb(Mg1/3Nb2/3)O3−XPbTiO3 Ceramics

Ceramic lead magnesium niobate–lead titanate ((1-x)PMN_-xPT) of different compositions has been prepared by the columbite precursor method. This study discusses compositions ranging from 0.94PMN–0.06PT to 0.60PM–N0.40PT, focusing on two areas of the (1-x)PMN_xPT system: compositions that exhibit electrostrictive behavior, and those that show piezoelectric behavior. In electrostrictive compositions where x is in the range of 0.06–0.20, the dielectric constant and electromechanical coupling factor dependencies on the bias field are evaluated. The optimal electromechanical properties are obtained with the composition 0.82PMN–0.18PT, measured at temperature T = T_m (the temperature of maximum dielectric constant) = 80°C and with a dc bias of 5 kV/cm. X–ray diffractometry is used to show that the (1-x)PMN_-xPT system has a compositionally wide two–phase region and that 0.655PMN–0.345PT is the morphotropic phase boundary (MPB) composition. Electromechanical property evaluation shows that the optimal piezoelectric properties (piezoelectric charge coefficient ( d₃₃ ) value of 720 pC/N, dielectric constant ( K ) value of 5400, and electromechanical planar and thickness coupling coefficient ( k_p and k_t , respectively) values of 62% and 46%, respectively) are obtained at the MPB composition.     

Small Reduction of the Piezoelectric d33 Response in Potassium Sodium Niobate Thick Films

We have investigated the electromechanical response of potassium sodium niobate (K_0.5Na_0.5NbO₃ or KNN) thick films. The high‐field strain hysteresis loops and weak‐field converse piezoelectric d₃₃ coefficient of the films were measured and compared with those of KNN bulk ceramics under the same electric field conditions. The converse d₃₃ values of the thick films and bulk ceramics were equal to 82.5 and 138 pm/V, respectively, at 0.4 kV/mm. The fundamental difference between the piezoelectric response of the KNN films and the ceramics was studied in terms of the effective (“clamped”) piezoelectric d₃₃ coefficient. The reduction in the piezoelectric d₃₃ coefficient of the KNN films, resulting from the clamping by the substrate, was compared to lead‐based ferroelectric thick films, including Pb(Zr,Ti)O₃ (PZT) and (1 ? x)Pb(Mg_1/3Nb_2/3)O₃?xPbTiO₃ (PMN‐PT). We propose a possible explanation, based on the particular elastic properties of KNN, for the small relative difference observed between the “clamped” and “unclamped” (“bulk”) d₃₃ of KNN, in comparison with lead‐based systems.     

Modified sepiolite/PVDF-HFP composite film with enhanced piezoelectric and dielectric properties

Flexible film with both piezoelectric and dielectric properties is considered to be a potential candidate for the energy conversion and storage devices. In this study, the Li⁺ and H₂O modified sepiolite/poly(vinylidene fluoride-co-hexafluoropropylene) (LiSEP-H₂O/PVDF-HFP) composite films with both good piezoelectric and dielectric properties were prepared by traditional coating process. When the H₂O content was 13 wt %, the LiSEP-H₂O/PVDF-HFP composite exhibited high d₃₃ of 32 and dielectric constant of 48. Moreover, the effects of the Li⁺ and adsorbed H₂O on the d₃₃, F(β), dielectric constant, short-circuit currents were discussed. The adsorbed H₂O enhanced the β-phase by the hydrogen bonds and Li⁺ improved the polarization to realize the composite film with increased piezoelectric and dielectric properties respectively. We expected the common modification to lead other clay minerals realizing the future applications in the adjustment of composites' electric properties. © 2019 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2020 , 137, 48412.     

Phase‐Composition‐Dependent Piezoelectric and Electromechanical Strain Properties in (Bi1/2Na1/2)TiO3–Ba(Ni1/2Nb1/2)O3 Lead‐Free Ceramics

New lead‐free perovskite solid solution ceramics of (1 ? x)(Bi_1/2Na_1/2)TiO₃–xBa(Ni_1/2Nb_1/2)O₃[(1?x)BNT–xBNN,x = 0.02–0.06) were prepared and their dielectric, ferroelectric, piezoelectric, and electromechanical properties were investigated as a function of the BNN content. The X‐ray diffraction results indicated that the addition of BNN has induced a morphotropic phase transformation from rhombohedral to pseudocubic symmetry approximately at x = 0.045, accompanying an evolution of dielectric relaxor behavior as characterized by enhanced dielectric diffuseness and frequency dispersion. In the proximity of the ferroelectric rhombohedral and pseudocubic phase coexistence zone, the x = 0.045 ceramics exhibited optimal piezoelectric and electromechanical coupling properties of d₃₃~121 pC/N and k_p~0.27 owing to decreased energy barriers for polarization switching. However, further addition of BNN could cause a decrease in freezing temperatures of polar nanoregions till the coexistence of nonergodic and ergodic relaxor phases occurred near room temperature, especially for the x = 0.05 sample which has negligible negative strains and thus show the maximum electrostrain of 0.3% under an external electric field of 7 kV/mm, but almost vanished piezoelectric properties. This was attributed to the fact that the induced long‐range ferroelectric order could reversibly switch back to its original ergodic state upon removal of external electric fields.